Antimetabolite agent combinations in the treatment of cancer

ABSTRACT

A method treating cancer in a subject comprises administering to the subject a therapeutically effective amount of an antimetabolite agent that induces formation of AP sites in cancer cells of the subjects and an amount AP endonuclease inhibitor effective to potentiate the cytotoxicity of the antimetabolite agent to the cancer cells.

RELATED APPLICATION

This application claims priority from U.S. Provisional Application No.61/170,344, filed Apr. 17, 2009, and U.S. patent application Ser. No.10/505,400, filed Aug. 19, 2004, the subject matter, which isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to compounds and methods fortreating neoplastic disorders in a subject, and more particularlyrelates to the use of antimetabolite antineoplastic agents and baseexcision repair inhibitors in the treatment of certain cancer and/orsolid tumors in a subject.

BACKGROUND

Cancer is a worldwide problem. Finding novel compositions and methodsfor the treatment of cancer is of vital interest. The treatment ofcancer falls into three general categories: chemotherapy, radiationtherapy and surgery. Often, therapies are combined since a combinationof therapies often increases the probability the cancer will beeradicated as compared to treatment strategies utilizing a singletherapy. Typically, the surgical excision of large tumor masses isfollowed by chemotherapy and/or radiation therapy.

Chemotherapeutic agents can work in a number of ways. For example,chemotherapeutics can work by interfering with cell cycle progression orby generating DNA strand breaks. If the cancer cell is not able toovercome the cell cycle blockage or cell injury caused by thetherapeutic compound, the cell will often die via apoptotic mechanisms.The use of a single chemotherapeutic agent in the treatment of cancer,with or without surgery or radiation, has several disadvantages.Commonly, cancer cells develop resistance to the chemotherapeutic agent.Such resistance results either in the requirement for higher dosages ofthe drug and/or the renewed spread of the cancer. Chemotherapeuticagents can be toxic to the patient. Therefore, there is a practicalupper limit to the amount that a patient can receive. However, if asecond agent can be developed to inhibit the pathway causing resistance,cancer cells may become susceptible to the effects of thechemotherapeutic agent.

The design of a drug to overcome resistance to the chemotherapeutictreatment of cancer should be approached with the goals of 1) finding acombination that reverses resistance and not merely improves theactivity of the chemotherapeutic with respect to activity on the tumor,and 2) finding a second drug that does not potentiate the toxic effectsof the first chemotherapeutic agent. These conditions require a greatdeal of empirical testing of agents known to have anticancer propertieswith agents that either may have anticancer properties, or that mayaugment the first agent in other ways. Unfortunately, such approacheshave thus far proven largely unsuccessful for combinations of manyanticancer agents.

Therefore, there exist insufficient therapies that reverse resistance tochemotherapy for the treatment of cancer.

SUMMARY OF THE INVENTION

The present invention relates to compositions and methods useful in thetreatment of certain cancers. In part, this application is based on theheretofore unknown recognition that certain molecules that target abasiclesions or AP (apurinic/apyrimidinic) sites in DNA improve, augment, orpotentiate the efficacy of antimetabolite antineoplastic agents. Inother embodiments, an inhibitor of the base excision pathway, such as anAP endonuclease inhibitor (e.g., methoxyamine), is combined with anantimetabolite antineoplastic agent. An antimetabolite antineoplasticagent is a chemotherapeutic with a similar structure to a substance (ametabolite) required for normal biochemical reactions, yet differentenough to interfere with the normal functions of cells, including celldivision.

In an aspect of the invention, a method of treating cancer in a subjectincludes administering to the subject a therapeutically effective amountof an antimetabolite agent that induces formation of AP sites in cancercells of the subject and an amount AP endonuclease inhibitor effectiveto potentiate the cytotoxicity of the antimetabolite agent to the cancercells. The AP endonuclease inhibitor can be selected from groupconsisting of methoxyamine, O-benzylohydroxylamine; ethylaminooxyacetate; aminooxyacetic acid; ethyl aminooxyacetate;H₂NOCHMeCO₂H; carboxymethoxyamine; aminooxyacetic acid;HN═C(NH₂)SCH₂CH₂ONH₂; H₂NO(CH₂)₃SC(NH₂)═NH; MeOC(O)CH(NH₂)CH₂ONH₂;H₂NOCH₂CH(NH₂)CO₂H; canaline; H₂NO(CH₂)₄ONH₂;O-(p-nitrobenzyl)hydroxylamine; 2-amino-4-(aminooxymethyl)thiazole;4-(aminooxymethyl)thiazole;O,O′-(o-phenylenedimethylene)dihydroxylamine; 2,4-dinitrophenoxyamine;O,O′-(m-phenylenedimethylene)dihydroxylamine;O,O′-(p-phenylenedimethylene)dihydroxylamine; H₂C═CHCH₂ONH₂;H₂NO(CH₂)₄ONH₂; H₃C—(CH₂)₁₅—O—NH₂,2,2′-(1,2-ethanediyl)bis(3-aminooxy)butenedioic acid dimethyl diethylester;

-   -   a compound having a structure of Formula I:

-   -   wherein X is O or NH,    -   Y is O, S, or NH,    -   Z is absent or represents O, S, or NH, and    -   R represents a hydrogen or a hydrocarbon moiety,    -   and pharmaceutically acceptable salts thereof. In further        aspect, the AP endonuclease inhibitor can be methoxyamine.

The antimetabolite agent can include a nucleoside analog. The nucleosideanalog can be a hypomethylating agent and include, for example,5-aza-2′-deoxycytidine.

An anticancer agent can also be administered to the subject incombination with the antimetabolite agent and the AP endonucleaseinhibitor. The anticancer agent can include an alkylating agent. Anexample of an alkylating agent is temozolomide (TMZ).

The amount of antimetabolite agent administered to the subject can besubtherapeutic when administered in the absence of the AP endonucleaseinhibitor. The amount of the AP endonuclease inhibitor administered tothe subject can also be an amount sufficient to sensitize the cancercells without causing undue sensitization of normal cells.

The subject to which the antimetabolite agent and the AP endonucleaseinhibitor are administered can be selected as having a cancer at leastpartially resistant to treatment with antimetabolite agent alone. The APendonuclease inhibitor can be administered in an amount effective topotentiate the activity of the antimetabolite agent and overcome theresistance.

The cancer can be selected from the group consisting of carcinomas,melanomas, sarcomas, lymphomas, leukemias, astrocytomas, gliomas,malignant melanomas, chronic lymphocytic leukemia, lung cancers,colorectal cancers, ovarian cancers, pancreatic cancers, renal cancers,endometrial cancers, gastric cancers, liver cancers, head and neckcancers, and breast cancers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-B illustrate a schematic illustrations of (A) DNA repairmechanisms on DNA damage produced by an antimetabolite agent inaccordance with an aspect of the invention, and (B) the use ofmethoxyamine in inhibiting the repair mechanism.

FIGS. 2A-B illustrate charts showing dose and time dependant abasic siteformation in cancer cells following decitabine treatment.

FIG. 3 illustrates a plot of a clonogenic survival assay in cellstreated with decitabine and methoxyamine.

FIG. 4 illustrates a plot of clonogenic survival assay in cells treatedwith decitabine and methoxyamine.

FIG. 5 illustrates a chart showing apoptotic death is increased by acombined treatment of decitabine and methoxyamine.

FIG. 6 illustrates an immunoblot showing cell death markers measured inthe cells treated in FIG. 5.

FIG. 7 illustrates a plot showing a time line of tumor treatment withmethoxyamine and decitabine in human xenografts in mice.

FIG. 8 illustrates a plot of tumor volume in human xenografts treatedwith methoxyamine and decitabine as illustrated in FIG. 7.

FIG. 9 illustrates plots showing combined treatment of A375 xenograftsin mice treated with methoxyamine, decitabine, (5aza) and/or TMZ.

DETAILED DESCRIPTION Definitions

Unless indicated otherwise, the following terms have the followingmeanings when used herein and in the appended claims. Those terms thatare not defined below or elsewhere in the specification shall have theirart-recognized meaning.

The term “agent” and “drug” are used herein to mean chemical compounds,mixtures of chemical compounds, biological macromolecules, or extractsmade from biological materials, such as bacteria, plants, fungi, oranimal particularly mammalian) cells or tissues that are suspected ofhaving therapeutic properties. The agent or drug may be purified,substantially purified, or partially purified.

The term “antimetabolite” is used herein to mean a chemotherapeutic witha similar structure to a substance (a metabolite e.g., nucleoside)required for normal biochemical reactions, yet different enough tointerfere with the normal functions of cells, including cell division.

The term “antineoplastic” is used herein to mean a chemotherapeuticintended to inhibit or prevent the maturation and proliferation ofneoplasms (tumors) that may become malignant, by targeting the DNA.

The term “staining” is used herein to mean any number of processes knownto those in the field that are used to better visualize, distinguish oridentify a specific component(s) and/or feature(s) of a cell or cells.

The term “in operable combination”, “in operable order” and “operablylinked” is used herein to mean the linkage of nucleic acid sequences insuch a manner that a nucleic acid molecule capable of directing thetranscription of a given gene and/or the synthesis of a desired proteinmolecule is produced. The term also refers to the linkage of amino acidsequences in such a manner so that a functional protein is produced.

The term “morphology” is used herein to mean the visual appearance of acell or organism when viewed with the eye, a light microscope, aconfocal microscope or an electron microscope, as appropriate.

The term “subject,” “individual,” and “patient” are used interchangeablyherein to mean a human or other animal, such as farm animals orlaboratory animals (e.g., guinea pig or mice) capable of having cellcycle (influenced) determined diseases, either naturally occurring orinduced, including but not limited to cancer.

The term “reverses resistance” means that the use of a second agent incombination with a primary chemotherapeutic is able to produce asignificant decrease in tumor volume at a level of statisticalsignificance (e.g., p<0.05) when compared to tumor volume of untreatedtumor in the circumstance where the primary chemotherapeutic alone isunable to produce a statistically significant decrease in tumor volumecompared to tumor volume of untreated tumor. This generally applies totumor volume measurements made at a time when the untreated tumor isgrowing log rhythmically.

The term “potentiate” as used herein means to enhance or increase thebeneficial activity or efficacy of the anticancer agent over that whichwould be expected from the anticancer agent alone or the potentiatingagent alone.

The term “sensitize” as used herein means to alter cancer cells or tumorcells in a way that allows for more effective treatment of theassociated neoplastic disease with an antimetabolite agent, ananticancer agent, or radiation therapy. In some embodiments, normalcells are not affected to an extent that causes the normal cells to beunduly injured by the antimetabolite, chemotherapy, or radiationtherapy.

The term “synergistic effect” as used herein means the combined effectof two or more anticancer agents or chemotherapy drugs can be greaterthan the sum of the separate effects of the anticancer agents orchemotherapy drugs alone. For example, the combined effect of a BERinhibitor, such as methoxyamine, and an antimetabolite agent, such asdecitabine, can be greater than the sum of the separate effects ofmethoxyamine and decitabine alone.

The term “therapeutically effective amount” means the amount of thesubject compound that will elicit a desired response, for example, abiological or medical response of a tissue, system, animal, or humanthat is sought, for example, by a researcher, veterinarian, medicaldoctor, or other clinician.

The term “wild type” (wt) cell or cell line is used herein, for purposesof the specification and claims, to mean a cell or cell line thatretains the characteristics normally associated with that type of cellor cell line for the physiological process or morphologicalcharacteristic that is being examined. It is permissible for the cell orcell line to have non-wild type characteristics for physiologicalprocess or morphological characteristics that are not being examined aslong as they do not appreciably affect the process or characteristicbeing examined.

The term “pharmaceutically acceptable salt” refers to a salt of acompound that does not cause significant irritation to an organism towhich it is administered and does not abrogate the biological activityand properties of the compound. In some embodiments, the salt is an acidaddition salt of the compound. Pharmaceutical salts can be obtained byreacting a compound with inorganic acids such as hydrohalic acid (e.g.,hydrochloric acid or hydrobromic acid), sulfuric acid, nitric acid,phosphoric acid and the like. Pharmaceutical salts can also be obtainedby reacting a compound with an organic acid such as aliphatic oraromatic carboxylic or sulfonic acids, for example acetic, succinic,lactic, malic, tartaric, citric, ascorbic, nicotinic, methanesulfonic,ethanesulfonic, p-toluensulfonic, salicylic or naphthalenesulfonic acid.Pharmaceutical salts can also be obtained by reacting a compound with abase to form a salt such as an ammonium salt, an alkali metal salt, suchas a sodium or a potassium salt, an alkaline earth metal salt, such as acalcium or a magnesium salt, a salt of organic bases such asdicyclohexylamine, N-methyl-D-glucamine, tris(hydroxymethyl)methylamine,C₁-C₇ alkylamine, cyclohexylamine, triethanolamine, ethylenediamine, andsalts with amino acids such as arginine, lysine, and the like.

The term “small molecule” refers to a low molecular weight organiccompound, which is by definition not a polymer. The small molecule canbind with high affinity to a biopolymer, such as protein, nucleic acid,or polysaccharide and in some instances alter the activity or functionof the biopolymer. The upper molecular weight limit for a small moleculeis about 800 Daltons, which allows for the possibility to rapidlydiffuse across cell membranes so that they can reach intracellular sitesof action. In addition, this molecular weight cutoff can be a conditionfor oral bioavailability.

The term “analog” refers to a molecule that differs in chemicalstructure from a parent compound, for example a homolog (differing by anincrement in the chemical structure, such as a difference in the lengthof an alkyl chain), a molecular fragment, a structure that differs byone or more functional groups, a change in ionization. Structuralanalogs are often found using quantitative structure activityrelationships (QSAR), with techniques such as those disclosed inRemington (The Science and Practice of Pharmacology, 19th Edition(1995), chapter 28).

The term “derivative” refers to a substance related to a base structure,and theoretically derivable from the base structure.

The term “mimetic” refers to a biomolecule that mimics the activity ofanother biologically active molecule.

The present invention relates to compositions and methods of treatingcancer in subject by administering to the subject a first formulationcomprising an antimetabolite antineoplastic agent that induces formationof AP sites in cancer cells of the subject and a second formulationcomprising an AP endonuclease inhibitor that is effective to potentiatethe cytotoxicity of the antimetabolite agent to the cancer cells.

Injury to DNA is minimized by enzymes that recognize errors, removethem, and replace the damaged DNA with corrected nucleotides. DNA damageoccurs when a single-strand break is introduced, a base is removedleaving its former partner unpaired, a base is covalently modified, abase is converted into another that is not appropriately paired with thepartner base, or a covalent link is introduced between bases on oppositestrands. Excision repair systems remove the mispaired or damaged basefrom the DNA strand and then synthesize new DNA to replace it. Baseexcision repair (BER) is initiated during replication of DNA and allowsfor correction of damaged bases/mispaired bases prior to completion ofreplication.

Base excision repair (BER) is initiated by a DNA glycosylase thatremoves N-glycosidic (base-sugar) bonds, liberating the damaged base andgenerating an abasic site (e.g., an apurinic or apyrimidinic (AP) site).An apurinic or apyrimidinic (AP) site results from the loss of a purineor pyrimidine residue, respectively, from DNA (deoxyribonucleic acid).Uracil residues can form from the spontaneous deamination of cytosineand can lead to a C→T transition if unrepaired. There is also aglycosylase that recognizes and excises hypoxanthine, the deaminationproduct of adenine. Other glycosylases remove alkylated bases (such as3-methyladenine, 3-methylguanine, and 7-methylguanine), ring-openedpurines, oxidatively damaged bases, and in some organisms, UVphotodimers.

The AP site is further processed by a 5′-3′ endonuclease (APendonuclease (APE)) that incises the phosphodiester bond on both sidesof the damaged purine or pyrimidine base. The AP endonucleases introducechain breaks by cleaving the phosphodiester bonds at the AP sites.

PARP aids in processing of DNA strand breaks induced during BER. PARP isa DNA nick surveillance protein that binds weakly to BER intermediateswhen single-nucleotide BER proceeds normally to completion. In contrast,when single nucleotide BER is stalled by a block in the excision step,PARP binds strongly to the BER intermediate, along with AP endonuclease(APE), DNA pol 3, and FEN-1.

In mammalian cells, the 5′-deoxyribose sugar phosphate is removed by theintrinsic AP lyase (dRP) activity of DNA polymerase 3 (pol 0). DNApolymerase enzyme also fills the gaps with new nucleotides.

Finally, DNA ligase covalently links the 3′ end of the new material tothe old material. Thus, the wild-type sequence is restored.

Topoisomerases I and II are also involved in DNA repair, as theyrecognize spontaneous AP sites and form stable cleavable complexes.Topoisomerase II inhibitors promote DNA cleavage and other chromosomalaberrations, including sister chromatid exchanges.

The antimetabolite antineoplastic agents (or antimetabolite agents) inaccordance with the present invention are agent compounds, or smallmolecules that interfere with the replication, translation ortranscription of nucleic acids and induce formation of AP sites incancer cells of a subject. In one embodiment of the present invention,the antimetabolite agent can include a nucleoside analog that whenadministered to a cancer cell of a subject induces formation of AP sitesin the cancer cells. Nucleoside analogs are antimetabolites that mimicnucleosides. FIG. 1 illustrates that antimetabolite nucleoside analogsincorporated into DNA are recognized and processed by the base excisionrepair (BER) pathway and induce formation of AP sites. The inhibition ofthe BER pathway with an AP endonuclease inhibitor (e.g., methoxyamine(mx)) can potentiate the cytoxic effects of the nucleoside analogadministered to cancer cells.

One example of a nucleoside analog that is an antimetabolite and inducesformation of an AP site is 5-fluorouracil (5-FU). 5-Fluorouracil hasbeen used clinically in the treatment of malignant tumors, including,for example, carcinomas, sarcomas, skin cancer, cancer of the digestiveorgans, and breast cancer. 5-Fluorouracil, however, can cause seriousadverse reactions such as nausea, alopecia, diarrhea, stomatitis,leukocytic thrombocytopenia, anorexia, pigmentation, and edema.Derivatives of 5-fluorouracil with anti-cancer activity have beendescribed in U.S. Pat. No. 4,336,381. Further 5-FU derivatives have beendescribed in the following patents listed in JP 50-50383, JP 50-50384,JP 50-64281, JP 51-146482, and JP 53-84981 hereby individuallyincorporated by reference herein.

In some embodiments of the invention, the nucleoside analog that inducesformation of AP sites in cancer cells of the subject can be ahypomethylating agent. As used herein, the term “hypomethylating agent”refers to an agent that reduces or reverses DNA methylation, either at aspecific site (e.g., a specific CpG island) or generally throughout agenome. Hypomethylating agents can be referred to as possessing“hypomethylating activity.” By way of example, such activity is measuredby determining the methylation state and/or level of a specific DNAmolecule or site therein, or the general methylation state of a cell, onparallel samples that have and have not been treated with thehypomethylating agent (or putative hypomethylation agent). A reductionin methylation in the treated (versus the untreated) sample indicatesthat the agent has hypomethylating activity.

An example of a nucleoside analog that is a hypomethylating agent is4-amino-1-(2-deoxy-b-D-erythro-pentofuranosyl)-1,3,5-triazin-2(1H)-one(e.g., 5-aza-2′-deoxycytidine, decitabine, or DACOGEN, Eisai Inc.,Woodcliff Lake, N.J.). Decitabine is an antagonist of its relatednatural nucleoside, deoxycytidine. The only structural differencebetween these two compounds is the presence of a nitrogen at position 5of the cytosine ring in decitabine as compared to a carbon at thisposition for deoxycytidine. Two isomeric forms of decitabine can bedistinguished. The β-anomer is the active form. The modes ofdecomposition of decitabine in aqueous solution are (a) conversion ofthe active β-anomer to the inactive .alpha.-anomer (Pompon et al. (1987)J. Chromat. 388:113-122); (b) ring cleavage of the aza-pyrimidine ringto form N-(formylamidino)-N′-.beta.-D-2′-deoxy(ribofuranosy)-urea(Mojaverian and Repta (1984) J. Pharm. Pharmacol. 36:728-733); and (c)subsequent forming of guanidine compounds (Kissinger and Stemm (1986) J.Chromat. 353:309-318).

Decitabine possesses multiple pharmacological characteristics. At amolecular level, it is S-phase dependent for incorporation into DNA. Ata cellular level, decitabine can induce cell differentiation and exerthematological toxicity. Despite having a short half life in vivo,decitabine has excellent tissue distribution.

The most prominent function of decitabine is its ability to specificallyand potently inhibit DNA methylation. As described above for methylationof cytosine in CpG islands as an example, methylation of cytosine to5-methylcytosine occurs at the level of DNA. Inside the cell, decitabineis first converted into its active form, the phosphorylated5-aza-deoxycytidine, by deoxycytidine kinase, which is primarilysynthesized during the S phase of the cell cycle. The affinity ofdecitabine for the catalytical site of deoxycytidine kinase is similarto the natural substrate, deoxycytidine. Momparler et al. (1985)30:287-299. After conversion to its triphosphate form by deoxycytidinekinase, decitabine is incorporated into replicating DNA at a ratesimilar to that of the natural substrate, dCTP. Bouchard and Momparler(1983) Mol. Pharmacol. 24:109-114.

Incorporation of decitabine into the DNA strand has a hypomethylationeffect. Each class of differentiated cells has its own distinctmethylation pattern. After chromosomal duplication, in order to conservethis pattern of methylation, the 5-methylcytosine on the parental strandserves to direct methylation on the complementary daughter DNA strand.Substituting the carbon at the 5 position of the cytosine for a nitrogeninterferes with this normal process of DNA methylation. The replacementof 5-methylcytosine with decitabine at a specific site of methylationproduces an irreversible inactivation of DNA methyltransferase,presumably due to formation of a covalent bond between the enzyme anddecitabine. Juttermann et al. (1994) Proc. Natl. Acad. Sci. USA91:11797-11801. By specifically inhibiting DNA methyltransferase, theenzyme required for methylation, the aberrant methylation of the tumorsuppressor genes can be prevented. Moreover, once decitabine isincorporated into the DNA strand, the BER pathway is activated andformation of the AP site is induced.

Other examples, of nucleoside analogs that can be used to treat cancerare listed in U.S. Pat. No. 4,000,137, which is incorporated herein byreference. U.S. Pat. No. 4,000,137 discloses that the peroxidateoxidation product of inosine, adenosine, or cytidine with methanol orethanol has activity against lymphocytic leukemia. Cytosine arabinoside(also referred to as Cytarabin, araC, and Cytosar) is a nucleosideanalog of deoxycytidine that was first synthesized in 1950 andintroduced into clinical medicine in 1963. The primary action of araC isinhibition of nuclear DNA synthesis. Handschumacher, R. and Cheng, Y.,“Purine and Pyrimidine Antimetabolites”, Cancer Medicine, Chapter XV-1,3rd Edition, Edited by J. Holland, et al., Lea and Febigol, publishers.5-Azacytidine (VIDAZA, Celegene Corp., Summit, N.J.) is a cytidineanalog that is primarily used in the treatment of acute myelocyticleukemia and myelodysplastic syndrome.

In some embodiments of the invention, the antimetabolite agent can beselected from the group consisting of 5-Fu, 5-aza-deoxycytidine, and5-azacytidine. In another embodiment, the antimetabolite agent can bedecitabine and pharmaceutically acceptable salts thereof. For example,the decitabine can be the disodium salt.

The AP endonuclease inhibitor that potentiates the cytotoxicity of theantimetabolite agent can be a small molecule compound with a primaryamine group that forms a covalent linkage with and/or binds to analdehyde group of an AP site induced by the antimetabolic agent. Insingle-nucleotide BER, the deoxyribose phosphate (dRP) in the abasicsite is removed by the lyase activity of DNA pol P. Binding of the APendonuclease inhibitor to an aldehyde group can structurally alter theAP site so that AP endonuclease does not recognize the modified AP siteand/or prevent AP endonuclease-mediated cleavage of phosphodiesterbonds, thus blocking single nucleotide BER.

In an aspect of the invention, the reaction of the AP endonucleaseinhibitor with the aldehyde group in the cancer cells can be faster thanAP endonuclease to inhibit repair of DNA. Advantageously, administrationof the AP endonuclease inhibitor in combination with the antimetaboliteagent to tumor cells can bypass other resistance factors, such as MMRdefects and high MGMT activity in the tumor cells.

In some embodiments, the AP endonuclease inhibitor can be an aminooxysmall molecule compound that can react with an AP site faster than APendonuclease. One example of an aminooxy compound that that can reactwith an AP site faster than AP endonuclease is methoxyamine (MX) orsalts thereof. Methoxyamine when administered in combination with anantimetabolite agent, such as decitabine, to a subject with cancer canpotentiate the anticancer effect of the antimetabolite agent withoutadditive systemic toxicity.

In other embodiments the AP endonuclease inhibitor can be a smallmolecule having the formula I:

-   -   wherein X is O or NH,    -   Y is O, S, or NH,    -   Z is absent or represents O, S, or NH,    -   R represents a hydrogen or a hydrocarbon moiety, and    -   pharmaceutically acceptable salts thereof.

Other examples of small molecules primary amine compounds that can bindto AP sites and prevent APE-mediated cleavage of phosphodiester bondsinclude O-benzylhydroxylamine; ethyl aminooxyacetate; aminooxyaceticacid; ethyl aminooxyacetate; H₂N—OCHMeCO₂H; carboxymethoxyamine;aminooxyacetic acid; HN═C(NH₂)SCH₂CH₂ONH₂; H₂N—O(CH₂)₃SC(NH₂)═NH;MeOC(O)CH(NH₂)CH₂O—NH₂; H₂NOCH₂CH(NH₂)CO₂H; canaline; H₂N—O(CH₂)₄O—NH₂;O-(p-nitrobenzyl)hydroxylamine; 2-amino-4-(aminooxymethyl)thiazole;4-(aminooxymethyl)thiazole;O,O′-(o-phenylenedimethylene)dihydroxylamine; 2,4-dinitrophenoxyamine;O,O′-(m-phenylenedimethylene)dihydroxylamine;O,O′-(p-phenylenedimethylene)dihydroxylamine; H₂C═CHCH₂O—NH₂;H₂N—O(CH₂)₄O—NH₂; H₃C(CH₂)₁₅O—NH₂,2,2′-(1,2-ethanediyl)bis(3-aminooxy)butenedioic acid dimethyl diethylester; compounds having any of the following structures:

-   -   and pharmaceutically acceptable salts of any of these compounds.

Still other examples of small molecules primary amine compounds that canbind to AP sites and prevent APE-mediated cleavage of phosphodiesterbonds can be identified using a high-throughput screening assaydescribed below. The high-throughput screening assay includes twomolecular reaction assays:

1. Analysis of chemical—modified AP Sites assayed by Aldehyde ReactiveProbe (ARP). This is a competitive assay to measure the reactivity withAP site between ARP reagent (Dojindo Molecular Technologies Inc.,Gaithersburg, Md.) and the screening compounds. ARP and MX have asimilar reactivity with AP sites. They react specifically with analdehyde group that is open ring form of the AP sites. Thus, this assaywill allow identification of compounds with potential to block AP siterepair based on the binding affinity and efficiency to AP sites ofscreening compounds compared to ARP and MX.

a. AP site standard preparation: AP sites were produced in a calf thymusDNA by heat/acid-buffer solution. Intact calf thymus DNA was added tosodium citrate buffer (10 mM sodium citrate containing 10 mMNaH.sub.2PO.sub.4 and 10 mM NaCl, pH 5.0) and held at 70° C. for 30 min.The reaction was stopped by chilling rapidly on ice, and the DNA wasthen precipitated with cold ethanol, washed with 70% ethanol, dried, andresuspended in sterilized distilled water.

b. AP-DNA (15 pg) was incubated with test compounds at differentconcentrations at 37° C. for 30 min prior to ARP (1 mM) or ARP alone(Dojindo Molecular Technologies Inc., Gaithersburg, Md.) for 30 min.After precipitation and wash with ethanol, DNA was resuspended in TEbuffer (10 mM Tris-HCl, 1 mM EDTA, pH 7.2). DNA was heat-denatured at100° C. for 5 min, quickly chilled on ice, and mixed with an equalamount of 2 M ammonium acetate. The single-stranded DNA was thenimmobilized on a BAS-85 NC membrane (Schleicher and Schuell) using avacuum filter device (Schleicher and Schuell). The NC membrane wasincubated with streptavidinconjugated horseradish peroxidase (BioGenix)at room temperature for 30 min. After NC membrane was rinsed withwashing buffer containing NaCl (0.26 M), EDTA (1 mM), Tris-HCl (20 mM),and Tween 20 (1%), ARP-AP sites are visualized with ECL reagents(Amersham Corp.) and quantitated by scanning densitometer.

2. AP sites cleavaged by AP-endonuclease (APE). This assay confirms thatAP sites modified by potential BER inhibitors are resistant to cleavageby APE, (Trevigen, Gaithersburg, Md.) a BER protein. The assay may beperformed as follows (see also FIGS. 23A and B):

a. AP site is prepared by replacing single nucleoside with deoxyuridinein duplex oligonucleotides (40 mer).

b. Regular AP site is produced in the duplex oligonucleotides by humanuracil DNA glycosylase (LIDGase, Trevigen, Gaithersburg, Md.) to removethe uracil residue.

c. To generate MX-adducted AP site substrates: the UDG-treated duplexoligonucleotides are mixed with 10 mM MX in buffer containing 10 mMKPO4, pH 7.1 and incubated at 37° C. After 30 min, the substrates arerecovered by ethanol precipitation, lyophilized, resuspended in water,and stored at −20 C.

d. APE-cleavage reaction: DNA substrates containing either regularAP-sites or chemical modified AP sites are incubated with APE (Trevigen,Gaithersburg, Md.) for 30 min and reactants are precipitated with 100%cold ethanol, washed with 70% ethanol and resuspended in TE buffer. Thereactants are resolved by denaturing 20% polyacrylamide gelelectrophoresis and visualized by silver staining (Silver Staining Kit,Pharmacia Biotech).

In some embodiments, the antimetabolite administered in combination withthe AP endonuclease inhibitor can be used to treat a patient or subjecthaving a neoplastic disease. For example, the neoplastic disease can bea cancer selected from the group consisting of carcinomas, melanomas,sarcomas, lymphomas, leukemias, astrocytomas, gliomas, malignantmelanomas, chronic lymphocytic leukemia, lung cancers, prostate cancer,colorectal cancers, ovarian cancers, pancreatic cancers, renal cancers,endometrial cancers, gastric cancers, liver cancers, head and neckcancers.

In some embodiments, the antimetabolite agent and the AP endonucleaseinhibitor can be administered to an individual in combination. Forexample, the AP endonuclease inhibitor and the antimetabolite agent canbe administered to an individual together in a parenteral formulation.Alternatively, the AP endonuclease inhibitor and the antimetaboliteagent can be administered to an individual together in an oralformulation, such as a solid dosage formulation.

In some embodiments, the AP endonuclease inhibitor and theantimetabolite agent can be administered to an individual sequentially,where the individual is first given the antimetabolite agent and thengiven the AP endonuclease inhibitor. For example, the individual can begiven the antimetabolite agent in a parenteral formulation, such as anintravenous formulation, or an oral formulation, such as a solid dosageformulation and then given the AP endonuclease inhibitor in a parenteralformulation, such as an intravenous formulation, or an oral formulation,such as a solid dosage formulation.

Alternatively, in some embodiments, the AP endonuclease inhibitor andthe antimetabolite agent can be administered to an individualsequentially, where the individual is first given the AP endonucleaseinhibitor and then given the antimetabolite agent. For example, theindividual can be given the AP endonuclease inhibitor in a parenteralformulation, such as an intravenous formulation, or an oral formulation,such as a solid dosage formulation and then given the antimetaboliteagent in a parenteral formulation, such as an intravenous formulation,or an oral formulation, such as a solid dosage formulation.

In some embodiments, the antimetabolite agent and the AP endonucleaseinhibitor can create an anticancer effect greater than that of theseparate anticancer effects of the individual agents. For example, thecombined anticancer effect of the antimetabolite agent and the APendonuclease inhibitor can be greater than the added anticancer effectof the antimetabolite agent and the AP endonuclease inhibitor when usedindividually.

In certain embodiments, the present invention contemplates the use of anantimetabolite agent, such as decitabine, that induces the formation ofAP sites and an AP endonuclease inhibitor, such as methoxyamine.

In some embodiments, the antimetabolite agent can be administered in adose of from about 10 mg/m² to about 5,000 mg/m² body surface area. Forexample, the dose can be from about 20 mg/m² to about 200 mg/m² bodysurface area; the dose can be from about 150 mg/m² to about 500 mg/m²body surface area; the dose can be from about 400 mg/m² to about 1000mg/m² body surface area; the dose can be from about 900 mg/m² to about5,000 mg/m² body surface area; the dose can be from about 200 mg/m² toabout 1,000 mg/m² body surface area; or the dose can be from about 500mg/m² to about 600 mg/m² body surface area. In some embodiments, theantimetabolite agent can be decitabine and pharmaceutically acceptablesalts thereof.

In some embodiments, the ratio of AP endonuclease inhibitor toantimetabolite agent can be from about 1 to about 1:10000. For example,ratio of AP endonuclease inhibitor to antimetabolite agent can be fromabout 1:2 to about 1:100; the ratio of AP endonuclease inhibitor toantimetabolite agent can be from about 1:50 to about 1:500; the ratio ofAP endonuclease inhibitor to antimetabolite agent can be from about1:450 to about 1:10000; the ratio of AP endonuclease inhibitor toantimetabolite agent can be from about 1:5 to about 1:500; the ratio ofAP endonuclease inhibitor to antimetabolite agent can be from about 1:10to about 1:50; the ratio of AP endonuclease inhibitor to antimetaboliteagent can be from about 1:15 to about 1:40; or the ratio of APendonuclease inhibitor to antimetabolite agent can be from about 1:20 toabout 1:30.

In some embodiments, an AP endonuclease inhibitor is administered in anamount sufficient to enhance or increase the effect of an antimetaboliteagent.

Some embodiments provide a method of treating cancer, comprisingproviding a first formulation containing an antimetabolite agent and asecond formulation containing an AP endonuclease inhibitor that can beadministered separately or as a combined formulation selecting a subjectdiagnosed with cancer, wherein the cancer is resistant to treatment withthe antimetabolite agent alone or in combination with other anticanceragents; administering said first formulation and said secondformulation; wherein the amount of the first formulation and the amountof the second formulation can be in a amount that when administered tosaid subject the anticancer effect can be greater than the anticancereffect of the first formulation alone.

In other embodiments, the AP endonuclease inhibitor and theantimetabolite agent can be administered to subject in combination withat least one other BER inhibitor. In an aspect of the invention, the atleast one other BER inhibitor can include a PARP inhibitor. Examples ofPARP inhibitors are 4-amino-1,8-naphthalimide (ANI), PD128763, 3-AB,6-AN, and 8-hydroxy-2-methyl-quinazolin-4-[3H]one (NU-1025).

Other examples of BER inhibitors that can be administered to the subjectin combination with the antimetabolite agent and the AP endonucleaseinhibitor include DNA polymerase inhibitors (e.g., DNA polymerase β, γor ε), such as prunasin, aphidicolin, 2′,3′-dideoxycytidine triphosphate(ddCTP), 2′,3′-dideoxythymidine triphosphate (ddTTP),2′,3′-dideoxyadenosine triphosphate (ddATP), 2′,3′-dideoxyguanosinetriphosphate (ddGTP), 1-beta-D-arabinofuranosylcytosine (Ara-C),caffeine, arabinocytidine, and bleomycin.

Still other examples of BER inhibitors that can be administered to thesubject in combination with the antimetabolite agent and the APendonuclease inhibitor include DNA ligase inhibitors (e.g., DNA ligaseI, II, or III), such as ursolic and oleanolic acids, aleuritolic acid,protolichesterinic acid, swertifrancheside, fulvoplumierin, fagaroninechloride, and bleomycin. XRCC1 is the protein partner of DNA ligase III,and inhibitors of XRCC1, such as 3-AB, are useful as BER inhibitors aswell.

Further examples of BER inhibitors that can be administered to thesubject in combination with the antimetabolite agent and the APendonuclease inhibitor include topoisomerase II inhibitors.Topoisomerase inhibitors induce DNA cleavage and other chromosomalaberrations, including sister chromatid exchanges. Compounds useful asBER inhibitors also include topoisomerase II inhibitors, such asetoposide (VP-16, VP-16-123),meso-4,4′-(2,3-butanediyl)-bis-(2,6-piperazinedione) (ICRF-193, abisdioxopiperazine), doxorubicin (DOX), L amsacrine(4′,9-acridinylaminomethanesulfon-m-anisidide; mAMSA), pazelliptine,nalidixic acid, oxolinic acid, novobiocin, coumermycin A1, fostriecin,teniposide, mitoxantrone, daunorubicin,N-[2-dimethylamino)ethyl]acridine-4-carboxamide (DACA), merbarone,quinacrine, ellipticines, epipodophyllotoxins, ethidium bromide,epirubicin, pirarubicin, 3′-deamino-3′-morpholino-13-deoxo-10-hydroxycaminomycin; 2″,3″-bis pentafluorophenoxyacetyl-4′,6′-ethylidene-beta-Dglucoside of 4′-phosphate-4′-dimethylepipodophyollotoxin 2N-methylglucamine salt (F11782; a fluorinated lipophilic epipodophylloid),adriamycin, actinomycin D, anthracyclines (such as9-aminoanthracycline), and pyrazoloacridine (PZA). Topoisomerase Iinhibitors, such as camptothecin and topotecan can also be used as BERinhibitors.

In some embodiments, other enzyme inhibitors, whether known in the artor hereafter identified, as well as inhibitors of other elements of theBER pathway, such as DNA alkyltransferase, may be employed incompositions and methods without departing from the scope and spirit ofthe present embodiments.

In certain embodiments, the present invention contemplates the use of 1)a PARP inhibitor, 2) an antimetabolite agent that induces the formationof AP sites, such as decitabine, and 3) an AP endonuclease inhibitor,such as methoxyamine.

In still other embodiments, the AP endonuclease inhibitor and theantimetabolite agent can be administered to subject in combination withat least one other anticancer agent that induces formation of AP sites.Anticancer agents that induce the formation of AP sites includeintercalating agents, such as bleomycin, adriamycin, quinacrine,echinomycin (a quinoxaline antibiotic), and anthrapyrazoles.

Radiation, such as gamma radiation, UVA, and UVB, can be used togenerate AP sites according to the methods of the invention. Ultravioletlight is absorbed in DNA with the formation of UV-specific di-pyrimidinephotoproducts. Exposure to gamma irradiation, UVA, and UVB can inducedamaged pyrimidine photodimers Anticancer agents that induce theformation of AP sites can also include DNA oxidizing agents, such ashydrogen peroxide.

Anticancer agents that induce the formation of AP sites can furtherinclude alkylating agents such, as temozolomide (TMZ),1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), MeOSO₂(CH₂)₂-lexitropsin(Me-Lex), cis-diamminedichloroplatinum II (cisplat; cis-DDP), mitomycinbioreductive alkylating agents, quinones, streptozotocin,cyclophosphamide, nitrogen mustard family members such as chloroambucil,pentostatin (and related purine analogs), fludarabine, bendamustinehydrochloride, chloroethylating nitrosoureas (e.g., lomustine,fotemustine, cystemustine), dacarbazine (DTIC), and procarbazine. Incertain embodiments, the alkylating agent is a nitrosoruea, such as amustine.

Alkylating agents can function by adding methyl groups to DNA,cross-linking macromolecules essential for cell division, and linkingguanine bases in DNA through their N⁷ atoms. Both inter- andintra-strand cross-links can be mediated by alkylating agents.Inter-strand cross-links prevent the separation of the DNA strandsnecessary for cell division, and by being more difficult to repair,constitute the more lethal lesion.

In certain embodiments, the anticancer agent is selected fromradiosensitizers such as 5-iodo-2′-deoxyuridine (IUdR), fludarabine,6-thioguanine, hypoxanthine, uracil, ecteinascidin-743, and camptothecinand analogs thereof.

In certain embodiments, the anticancer agent is not temozolomide. Incertain embodiments, the anticancer agent is not BCNU. In certainembodiments, the anticancer agent is not PE128723, 6-AN, 3-AB, BCNU, ortemozolomide

It will be appreciated that compositions or formulations provided hereinmay be in any form, which allows for the composition to be administeredto a patient. For example, the composition may be in the form of asolid, liquid or gas (e.g., aerosol). Other routes of administrationinclude, without limitation, oral, topical, parenteral (e.g.,sublingually or buccally), sublingual, rectal, vaginal, and intranasal.The term parenteral as used herein includes subcutaneous injections,intravenous, intramuscular, intrasternal, intracavemous, intrathecal,intrameatal, intraurethral injection or infusion techniques. Thepharmaceutical composition is formulated so as to allow the activeingredients contained therein to be bioavailable upon administration ofthe composition to a patient. Compositions that will be administered toa patient take the form of one or more dosage units, where for example,a tablet may be a single dosage unit, and a container of one or morecompounds of the invention in aerosol form may hold a plurality ofdosage units.

In another aspect, the present invention relates to a pharmaceuticalcomposition comprising physiologically acceptable surface active agents,carriers, diluents, excipients, smoothing agents, suspension agents,film forming substances, and coating assistants, or a combinationthereof; and a compound disclosed herein. Acceptable carriers ordiluents for therapeutic use are well known in the pharmaceutical art,and are described, for example, in Remington's Pharmaceutical Sciences,18th Ed., Mack Publishing Co., Easton, Pa. (1990), which is incorporatedherein by reference in its entirety. Preservatives, stabilizers, dyes,sweeteners, fragrances, flavoring agents, and the like may be providedin the pharmaceutical composition. For example, sodium benzoate,ascorbic acid and esters of p-hydroxybenzoic acid may be added aspreservatives. In addition, antioxidants and suspending agents may beused. In various embodiments, alcohols, esters, sulfated aliphaticalcohols, and the like may be used as surface active agents; sucrose,glucose, lactose, starch, crystallized cellulose, mannitol, lightanhydrous silicate, magnesium aluminate, magnesium methasilicatealuminate, synthetic aluminum silicate, calcium carbonate, sodium acidcarbonate, calcium hydrogen phosphate, calcium carboxymethyl cellulose,and the like may be used as excipients; magnesium stearate, talc,hardened oil and the like may be used as smoothing agents; coconut oil,olive oil, sesame oil, peanut oil, soya may be used as suspension agentsor lubricants; cellulose acetate phthalate as a derivative of acarbohydrate such as cellulose or sugar, or methylacetate-methacrylatecopolymer as a derivative of polyvinyl may be used as suspension agents;and plasticizers such as ester phthalates and the like may be used assuspension agents.

The term “pharmaceutical composition” refers to a mixture of a compounddisclosed herein with other chemical components, such as diluents orcarriers. The pharmaceutical composition facilitates administration ofthe compound to an organism. Multiple techniques of administering acompound exist in the art including, but not limited to, oral,injection, aerosol, parenteral, and topical administration.Pharmaceutical compositions can also be obtained by reacting compoundswith inorganic or organic acids such as hydrochloric acid, hydrobromicacid, sulfuric acid, nitric acid, phosphoric acid, methanesulfonic acid,ethanesulfonic acid, p-toluenesulfonic acid, salicylic acid and thelike.

The term “carrier” defines a chemical compound that facilitates theincorporation of a compound into cells or tissues. For example, dimethylsulfoxide (DMSO) is a commonly utilized carrier as it facilitates theuptake of many organic compounds into the cells or tissues of anorganism.

The term “diluent” defines chemical compounds diluted in water that willdissolve the compound of interest as well as stabilize the biologicallyactive form of the compound. Salts dissolved in buffered solutions areutilized as diluents in the art. One commonly used buffered solution isphosphate buffered saline because it mimics the salt conditions of humanblood. Since buffer salts can control the pH of a solution at lowconcentrations, a buffered diluent rarely modifies the biologicalactivity of a compound.

The term “physiologically acceptable” defines a carrier or diluent thatdoes not abrogate the biological activity and properties of thecompound.

The pharmaceutical compositions described herein can be administered toa human patient per se, or in pharmaceutical compositions where they aremixed with other active ingredients, as in combination therapy, orsuitable carriers or excipient(s). Techniques for formulation andadministration of the compounds of the instant application may be foundin “Remington's Pharmaceutical Sciences,” Mack Publishing Co., Easton,Pa., 18th edition, 1990.

Routes of administration may, for example, include oral, rectal,transmucosal, topical, or intestinal administration; parenteraldelivery, including intramuscular, subcutaneous, intravenous,intramedullary injections, as well as intrathecal, directintraventricular, intraperitoneal, intranasal, or intraocularinjections. The compounds can also be administered in sustained orcontrolled release dosage forms, including depot injections, osmoticpumps, pills, transdermal (including electrotransport) patches, and thelike, for prolonged and/or timed, pulsed administration at apredetermined rate.

The pharmaceutical compositions of the present invention may bemanufactured in a manner that is itself known, e.g., by means ofconventional mixing, dissolving, granulating, dragee-making, levigating,emulsifying, encapsulating, entrapping or tabletting processes.

Pharmaceutical compositions for use in accordance with the presentinvention thus may be formulated in conventional manner using one ormore physiologically acceptable carriers comprising excipients andauxiliaries, which facilitate processing of the active compounds intopreparations which can be used pharmaceutically. Proper formulation isdependent upon the route of administration chosen. Any of the well-knowntechniques, carriers, and excipients may be used as suitable and asunderstood in the art; e.g., in Remington's Pharmaceutical Sciences,above.

Injectables can be prepared in conventional forms, either as liquidsolutions or suspensions, solid forms suitable for solution orsuspension in liquid prior to injection, or as emulsions. Suitableexcipients are, for example, water, saline, dextrose, mannitol, lactose,lecithin, albumin, sodium glutamate, cysteine hydrochloride, and thelike. In addition, if desired, the injectable pharmaceuticalcompositions may contain minor amounts of nontoxic auxiliary substances,such as wetting agents, pH buffering agents, and the like.Physiologically compatible buffers include, but are not limited to,Hanks's solution, Ringer's solution, or physiological saline buffer. Ifdesired, absorption enhancing preparations (for example, liposomes), maybe utilized.

For transmucosal administration, penetrants appropriate to the barrierto be permeated may be used in the formulation.

Pharmaceutical formulations for parenteral administration, e.g., bybolus injection or continuous infusion, include aqueous solutions of theactive compounds in water-soluble form. Additionally, suspensions of theactive compounds may be prepared as appropriate oily injectionsuspensions. Suitable lipophilic solvents or vehicles include fatty oilssuch as sesame oil, or other organic oils such as soybean, grapefruit oralmond oils, or synthetic fatty acid esters, such as ethyl oleate ortriglycerides, or liposomes. Aqueous injection suspensions may containsubstances which increase the viscosity of the suspension, such assodium carboxymethyl cellulose, sorbitol, or dextran. Optionally, thesuspension may also contain suitable stabilizers or agents that increasethe solubility of the compounds to allow for the preparation of highlyconcentrated solutions. Formulations for injection may be presented inunit dosage form, e.g., in ampoules or in multi-dose containers, with anadded preservative. The compositions may take such forms as suspensions,solutions or emulsions in oily or aqueous vehicles, and may containformulatory agents such as suspending, stabilizing and/or dispersingagents. Alternatively, the active ingredient may be in powder form forconstitution with a suitable vehicle, e.g., sterile pyrogen-free water,before use.

For oral administration, the compounds can be formulated readily bycombining the active compounds with pharmaceutically acceptable carrierswell known in the art. Such carriers enable the compounds of theinvention to be formulated as tablets, pills, dragees, capsules,liquids, gels, syrups, slurries, suspensions and the like, for oralingestion by a patient to be treated. Pharmaceutical preparations fororal use can be obtained by combining the active compounds with solidexcipient, optionally grinding a resulting mixture, and processing themixture of granules, after adding suitable auxiliaries, if desired, toobtain tablets or dragee cores. Suitable excipients are, in particular,fillers such as sugars, including lactose, sucrose, mannitol, orsorbitol; cellulose preparations such as, for example, maize starch,wheat starch, rice starch, potato starch, gelatin, gum tragacanth,methyl cellulose, hydroxypropylmethyl-cellulose, sodiumcarboxymethylcellulose, and/or polyvinylpyrrolidone (PVP). If desired,disintegrating agents may be added, such as the cross-linked polyvinylpyrrolidone, agar, or alginic acid or a salt thereof such as sodiumalginate. Dragee cores are provided with suitable coatings. For thispurpose, concentrated sugar solutions may be used, which may optionallycontain gum arabic, talc, polyvinyl pyrrolidone, carbopol gel,polyethylene glycol, and/or titanium dioxide, lacquer solutions, andsuitable organic solvents or solvent mixtures. Dyestuffs or pigments maybe added to the tablets or dragee coatings for identification or tocharacterize different combinations of active compound doses. For thispurpose, concentrated sugar solutions may be used, which may optionallycontain gum arabic, talc, polyvinyl pyrrolidone, carbopol gel,polyethylene glycol, and/or titanium dioxide, lacquer solutions, andsuitable organic solvents or solvent mixtures. Dyestuffs or pigments maybe added to the tablets or dragee coatings for identification or tocharacterize different combinations of active compound doses.

Pharmaceutical preparations which can be used orally include push-fitcapsules made of gelatin, as well as soft, sealed capsules made ofgelatin and a plasticizer, such as glycerol or sorbitol. The push-fitcapsules can contain the active ingredients in admixture with fillersuch as lactose, binders such as starches, and/or lubricants such astalc or magnesium stearate and, optionally, stabilizers. In softcapsules, the active compounds may be dissolved or suspended in suitableliquids, such as fatty oils, liquid paraffin, or liquid polyethyleneglycols. In addition, stabilizers may be added. All formulations fororal administration should be in dosages suitable for suchadministration.

For buccal administration, the compositions may take the form of tabletsor lozenges formulated in conventional manner.

For administration by inhalation, the compounds for use according to thepresent invention are conveniently delivered in the form of an aerosolspray presentation from pressurized packs or a nebulizer, with the useof a suitable propellant, e.g., dichlorodifluoromethane,trichlorofluoromethane, dichlorotetrafluoroethane, carbon dioxide orother suitable gas. In the case of a pressurized aerosol the dosage unitmay be determined by providing a valve to deliver a metered amount.Capsules and cartridges of, e.g., gelatin for use in an inhaler orinsufflator may be formulated containing a powder mix of the compoundand a suitable powder base such as lactose or starch.

Further disclosed herein are various pharmaceutical compositions wellknown in the pharmaceutical art for uses that include intraocular,intranasal, and intraauricular delivery. Suitable penetrants for theseuses are generally known in the art. Pharmaceutical compositions forintraocular delivery include aqueous ophthalmic solutions of the activecompounds in water-soluble form, such as eyedrops, or in gellan gum(Shedden et al., Clin. Ther., 23(3):440-50 (2001)) or hydrogels (Mayeret al., Opthalmologica, 210(2):101-3 (1996)); ophthalmic ointments;ophthalmic suspensions, such as microparticulates, drug-containing smallpolymeric particles that are suspended in a liquid carrier medium(Joshi, A., J. Ocul. Pharmacol., 10(1):29-45 (1994)), lipid-solubleformulations (Alm et al., Prog. Clin. Biol. Res., 312:447-58 (1989)),and microspheres (Mordenti, Toxicol. Sci., 52(1):101-6 (1999)); andocular inserts. All of the above-mentioned references are incorporatedherein by reference in their entireties. Such suitable pharmaceuticalformulations are most often and preferably formulated to be sterile,isotonic and buffered for stability and comfort. Pharmaceuticalcompositions for intranasal delivery may also include drops and spraysoften prepared to simulate in many respects nasal secretions to ensuremaintenance of normal ciliary action. As disclosed in Remington'sPharmaceutical Sciences, 18th Ed., Mack Publishing Co., Easton, Pa.(1990), which is incorporated herein by reference in its entirety, andwell-known to those skilled in the art, suitable formulations are mostoften and preferably isotonic, slightly buffered to maintain a pH of 5.5to 6.5, and most often and preferably include antimicrobialpreservatives and appropriate drug stabilizers. Pharmaceuticalformulations for intraauricular delivery include suspensions andointments for topical application in the ear. Common solvents for suchaural formulations include glycerin and water.

The compounds may also be formulated in rectal compositions such assuppositories or retention enemas, e.g., containing conventionalsuppository bases such as cocoa butter or other glycerides.

In addition to the formulations described previously, the compounds mayalso be formulated as a depot preparation. Such long acting formulationsmay be administered by implantation (for example subcutaneously orintramuscularly) or by intramuscular injection. Thus, for example, thecompounds may be formulated with suitable polymeric or hydrophobicmaterials (for example as an emulsion in an acceptable oil) or ionexchange resins, or as sparingly soluble derivatives, for example, as asparingly soluble salt.

For hydrophobic compounds, a suitable pharmaceutical carrier may be acosolvent system comprising benzyl alcohol, a nonpolar surfactant, awater-miscible organic polymer, and an aqueous phase. A common cosolventsystem used is the VPD co-solvent system, which is a solution of 3% w/vbenzyl alcohol, 8% w/v of the nonpolar surfactant Polysorbate 80™, and65% w/v polyethylene glycol 300, made up to volume in absolute ethanol.Naturally, the proportions of a co-solvent system may be variedconsiderably without destroying its solubility and toxicitycharacteristics. Furthermore, the identity of the co-solvent componentsmay be varied: for example, other low-toxicity nonpolar surfactants maybe used instead of POLYSORBATE 80™; the fraction size of polyethyleneglycol may be varied; other biocompatible polymers may replacepolyethylene glycol, e.g., polyvinyl pyrrolidone; and other sugars orpolysaccharides may substitute for dextrose.

Alternatively, other delivery systems for hydrophobic pharmaceuticalcompounds may be employed. Liposomes and emulsions are well knownexamples of delivery vehicles or carriers for hydrophobic drugs. Certainorganic solvents such as dimethylsulfoxide also may be employed,although usually at the cost of greater toxicity. Additionally, thecompounds may be delivered using a sustained-release system, such assemipermeable matrices of solid hydrophobic polymers containing thetherapeutic agent. Various sustained-release materials have beenestablished and are well known by those skilled in the art.Sustained-release capsules may, depending on their chemical nature,release the compounds for a few weeks up to over 100 days. Depending onthe chemical nature and the biological stability of the therapeuticreagent, additional strategies for protein stabilization may beemployed.

Agents intended to be administered intracellularly may be administeredusing techniques well known to those of ordinary skill in the art. Forexample, such agents may be encapsulated into liposomes. All moleculespresent in an aqueous solution at the time of liposome formation areincorporated into the aqueous interior. The liposomal contents are bothprotected from the external micro-environment and, because liposomesfuse with cell membranes, are efficiently delivered into the cellcytoplasm. The liposome may be coated with a tissue-specific antibody.The liposomes will be targeted to and taken up selectively by thedesired organ. Alternatively, small hydrophobic organic molecules may bedirectly administered intracellularly.

Additional therapeutic or diagnostic agents may be incorporated into thepharmaceutical compositions. Alternatively or additionally,pharmaceutical compositions may be combined with other compositions thatcontain other therapeutic or diagnostic agents.

The compounds or pharmaceutical compositions may be administered to thepatient by any suitable means. Non-limiting examples of methods ofadministration include, among others, (a) administration though oralpathways, which administration includes administration in capsule,tablet, granule, spray, syrup, or other such forms; (b) administrationthrough non-oral pathways such as rectal, vaginal, intraurethral,intraocular, intranasal, or intraauricular, which administrationincludes administration as an aqueous suspension, an oily preparation orthe like or as a drip, spray, suppository, salve, ointment or the like;(c) administration via injection, subcutaneously, intraperitoneally,intravenously, intramuscularly, intradermally, intraorbitally,intracapsularly, intraspinally, intrasternally, or the like, includinginfusion pump delivery; (d) administration locally such as by injectiondirectly in the renal or cardiac area, e.g., by depot implantation; aswell as (e) administration topically; as deemed appropriate by those ofskill in the art for bringing the compound of the invention into contactwith living tissue.

Pharmaceutical compositions suitable for administration includecompositions where the active ingredients are contained in an amounteffective to achieve its intended purpose. The therapeutically effectiveamount of the compounds disclosed herein required as a dose will dependon the route of administration, the type of animal, including human,being treated, and the physical characteristics of the specific animalunder consideration. The dose can be tailored to achieve a desiredeffect, but will depend on such factors as weight, diet, concurrentmedication and other factors which those skilled in the medical artswill recognize. More specifically, a therapeutically effective amountmeans an amount of compound effective to prevent, alleviate orameliorate symptoms of disease or prolong the survival of the subjectbeing treated. Determination of a therapeutically effective amount iswell within the capability of those skilled in the art, especially inlight of the detailed disclosure provided herein.

As will be readily apparent to one skilled in the art, the useful invivo dosage to be administered and the particular mode of administrationwill vary depending upon the age, weight and mammalian species treated,the particular compounds employed, and the specific use for which thesecompounds are employed. The determination of effective dosage levels,that is the dosage levels necessary to achieve the desired result, canbe accomplished by one skilled in the art using routine pharmacologicalmethods. Typically, human clinical applications of products arecommenced at lower dosage levels, with dosage level being increaseduntil the desired effect is achieved. Alternatively, acceptable in vitrostudies can be used to establish useful doses and routes ofadministration of the compositions identified by the present methodsusing established pharmacological methods.

In non-human animal studies, applications of potential products arecommenced at higher dosage levels, with dosage being decreased until thedesired effect is no longer achieved or adverse side effects disappear.The dosage may range broadly, depending upon the desired effects and thetherapeutic indication. Typically, dosages may be between about 10microgram/kg and 100 mg/kg body weight, preferably between about 100microgram/kg and 10 mg/kg body weight. Alternatively, dosages may bebased and calculated upon the surface area of the patient, as understoodby those of skill in the art.

The exact formulation, route of administration and dosage for thepharmaceutical compositions of the present invention can be chosen bythe individual physician in view of the patient's condition. (See e.g.,Fingl et al. 1975, in “The Pharmacological Basis of Therapeutics”, whichis hereby incorporated herein by reference in its entirety, withparticular reference to Ch. 1, p. 1). Typically, the dose range of thecomposition administered to the patient can be from about 0.5 to 1000mg/kg of the patient's body weight. The dosage may be a single one or aseries of two or more given in the course of one or more days, as isneeded by the patient. In instances where human dosages for compoundshave been established for at least some condition, the present inventionwill use those same dosages, or dosages that are between about 0.1% and500%, more preferably between about 25% and 250% of the establishedhuman dosage. Where no human dosage is established, as will be the casefor newly-discovered pharmaceutical compounds, a suitable human dosagecan be inferred from ED₅₀ or ID₅₀ values, or other appropriate valuesderived from in vitro or in vivo studies, as qualified by toxicitystudies and efficacy studies in animals.

It should be noted that the attending physician would know how to andwhen to terminate, interrupt, or adjust administration due to toxicityor organ dysfunctions. Conversely, the attending physician would alsoknow to adjust treatment to higher levels if the clinical response werenot adequate (precluding toxicity). The magnitude of an administrateddose in the management of the disorder of interest will vary with theseverity of the condition to be treated and to the route ofadministration. The severity of the condition may, for example, beevaluated, in part, by standard prognostic evaluation methods. Further,the dose and perhaps dose frequency will also vary according to the age,body weight, and response of the individual patient. A programcomparable to that discussed above may be used in veterinary medicine.

Although the exact dosage will be determined on a drug-by-drug basis, inmost cases, some generalizations regarding the dosage can be made. Thedaily dosage regimen for an adult human patient may be, for example, anoral dose of between 0.1 mg/m² and 2000 mg/m² body surface area per dayof each active ingredient, typically between 1 mg/m² and 500 mg/m² bodysurface area per day, for example 5 mg/m² to 200 mg/m² body surface areaper day. In other embodiments, an intravenous, subcutaneous, orintramuscular dose of each active ingredient of between 0.01 mg/m² and100 mg/m² body surface area per day, typically between 0.1 μm² mg and 60mg/m² body surface area per day, for example, 1 mg/m² to 40 mg/m² bodysurface area per day can be used. In cases of administration of apharmaceutically acceptable salt, dosages may be calculated as the freebase. In some embodiments, the composition is administered 1 to 4 timesper day. Alternatively, the compositions of the invention may beadministered by continuous intravenous infusion, preferably at a dose ofeach active ingredient up to 1000 mg/m² body surface area per day. Aswill be understood by those of skill in the art, in certain situationsit may be necessary to administer the compounds disclosed herein inamounts that exceed, or even far exceed, the above-stated, preferreddosage range in order to effectively and aggressively treat particularlyaggressive diseases or infections. In some embodiments, the compoundswill be administered for a period of continuous therapy, for example fora week or more, or for months or years.

Dosage amount and interval may be adjusted individually to provideplasma levels of the active moiety, which are sufficient to maintain themodulating effects, or minimal effective concentration (MEC). The MECwill vary for each compound but can be estimated from in vitro data.Dosages necessary to achieve the MEC will depend on individualcharacteristics and route of administration. However, HPLC assays orbioassays can be used to determine plasma concentrations.

Dosage intervals can also be determined using MEC value. Compositionsshould be administered using a regimen, which maintains plasma levelsabove the MEC for 10-90% of the time, typically between 30-90% and mosttypically between 50-90%.

In cases of local administration or selective uptake, the effectivelocal concentration of the drug may not be related to plasmaconcentration.

The amount of composition administered may be dependent on the subjectbeing treated, on the subject's weight, the severity of the affliction,the manner of administration and the judgment of the prescribingphysician.

Compounds disclosed herein can be evaluated for efficacy and toxicityusing known methods. For example, the toxicology of a particularcompound, or of a subset of the L compounds, sharing certain chemicalmoieties, may be established by determining in vitro toxicity towards acell line, such as a mammalian, and preferably human, cell line. Theresults of such studies are often predictive of toxicity in animals,such as mammals, or more specifically, humans. Alternatively, thetoxicity of particular compounds in an animal model, such as mice, rats,rabbits, or monkeys, may be determined using known methods. The efficacyof a particular compound may be established using several recognizedmethods, such as in vitro methods, animal models, or human clinicaltrials. Recognized in vitro models exist for nearly every class ofcondition, including but not limited to cancer, cardiovascular disease,and various immune dysfunction. Similarly, acceptable animal models maybe used to establish efficacy of chemicals to treat such conditions.When selecting a model to determine efficacy, the skilled artisan can beguided by the state of the art to choose an appropriate model, dose, androute of administration, and regime. Of course, human clinical trialscan also be used to determine the efficacy of a compound in humans.

The compositions may, if desired, be presented in a pack or dispenserdevice, which may contain one or more unit dosage forms containing theactive ingredient. The pack may for example comprise metal or plasticfoil, such as a blister pack. The pack or dispenser device may beaccompanied by instructions for administration. The pack or dispensermay also be accompanied with a notice associated with the container inform prescribed by a governmental agency regulating the manufacture,use, or sale of pharmaceuticals, which notice is reflective of approvalby the agency of the form of the drug for human or veterinaryadministration. Such notice, for example, may be the labeling approvedby the U.S. Food and Drug Administration for prescription drugs, or theapproved product insert. Compositions comprising a compound of theinvention formulated in a compatible pharmaceutical carrier may also beprepared, placed in an appropriate container, and labeled for treatmentof an indicated condition.

Throughout the specification, any recitation of a particular compoundshould be understood to encompass that compound and any (other)pharmaceutically acceptable salts thereof.

Generally, the nomenclature used hereafter and the laboratory proceduresin cell culture, tissue culture, tumor biology, and molecular geneticsdescribed below are those well known and commonly employed in the art.Standard techniques are used for cell culture methods, experimentaldesign and compound formulation and nomenclature. Generally, chemicalreactions and purification steps are performed according to themanufacturer's specifications. The techniques and procedures aregenerally performed according to conventional methods in the art andvarious general references (see, generally, Sambrook et al. MolecularCloning. A Laboratory Manual, 2d ed. (1989) Cold Spring HarborLaboratory Press, Cold Spring Harbor, N.Y., and Current Protocols inMolecular Biology (1996) John Wiley and Sons, Inc., N.Y., which areincorporated herein by reference) which are provided throughout thisdocument. All the information contained therein is incorporated hereinby reference.

EXAMPLES Enhancement of Decitabine Cytotoxicity by Methoxyamine ViaInhibition of Base Excision Repair

Decitabine (5aza-2′deoxycytidine) is a nucleoside analog used for thetreatment of hematological malignancies. Previously, it was shown thatthe cytotoxic effect of low dose decitabine treatment is due toincorporation of its active metabolite, 5aza-2′deoxycytidinetriphosphate, into DNA leading to inhibition of DNA methylation bybinding irreversibly to DNA methyltransferases. We hypothesized thatincorporated 5aza-2′deoxycytidine (or its deaminated analog,5aza-2′deoxuridine) into DNA is also recognized and processed by thebase excision repair (BER) pathway. In this case, inhibition of BER bymethoxyamine (MX) would potentiate the cytotoxicity of decitabine. Weevaluated role of BER in decitabine cytotoxicity in colon cancer,melanoma cells, and primary acute myelogenos leukemia (AML) cells.Decitabine-induced abasic sites (AP-sites) were increased proportionallywith dose and duration of exposure (FIGS. 2 A-B). MX reduced the numberof available AP-sites up to 80% indicating formation of stable MX-boundAP-sites that have the potential to interrupt BER pathway. A similarcorrelation between decitabine dose and the AP-sites formed was observedafter in vitro exposure of primary AML cells to increase concentrationsof decitabine. MX was able to bind a significant percentage (up to 60%)of these AP sites. Decitabine cytotoxicity was potentiated by MX. Cellsurvival assays demonstrated a 4-fold decrease in the IC₅₀ fordecitabine when cells were co-treated with MX (IC_(50 dec)=4 μM andIC_(50 Dec+MX)=1 μM) (FIGS. 3-6). Apoptotic cell death measurementsusing Annexin V staining showed a 5-fold increase in cell death whencells following decitabine and MX. These events were accompanied by aconcomitant increase in cleavage of PARP, and in γH2AX. Moreover, MXenhanced decitabine-induced antitumor effect in mice bearing A375 humanmelanoma xenografts, as measured by tumor growth delay: 7 days (0.5mg/kg decitabine) versus 14 days (0.5 mg/kg decitabine plus 2 mg/kg MX)(FIGS. 7-9).

These studies not only suggests for the first time the role of BER inthe processing of incorporated decitabine, but they also provideinsights into a new and promising cancer therapeutic strategy ofcombining decutabine with MX to block BER.

Incorporation of Decitabine (5-Aza-dC) into DNA Activates the BERPathway and MX Potentiates 5-Aza-dC Cytotoxicity Through Blocking BER inMelanoma Cells

AP Sites Formed by 5-Aza-dC in Cells

To test whether the incorporation of 5-aza-dC activates the cellular BERpathway that removes 5-aza-dC as an abnormal base and generates an APsite, we examined the formation of AP sites in cellular DNA after cellswere exposed to various concentrations of 5-aza-dC (0, 0.1-20 μM) for 24h. The increase in formation of AP sites following treatment with5-aza-dC was observed, as detected by ARP reagent. We also examinedwhether MX recognizes and binds to AP sites produced by 5-aza-dC; if so,co-treatment with MX would reduce detectable AP sites. We haveintroduced that ARP reagent competitively binds to AP sites with MX, andit detects only free AP sites, but not MX-bound AP sites. As shown inFIGS. 2 A-B, AP sites increase proportionally with increasing 5-aza-dCconcentrations, from 0.1-5 μM. In contrast, relatively low levels of APsites were detected at higher concentrations (10 and 20 μM) of 5-aza-dC;probably, a higher percentage of cells were dead or dying after exposureto high doses of the drug. The combination with MX reduced AP sites. Thelevels of MX-bound AP sites were determined based on the differencesbetween the levels of AP sites in cells treated with 5-aza-dC alone andwith the combination of 5-aza-dC and MX. The clonogenic survival assays(FIGS. 3-4) showed that MX enhanced 5-aza-dC killing effect by 5 folds.The IC90 value was 4 M for TMZ combined with MX, compared to 20 μM for5-aza-dC alone (FIGS. 3-4).

The Combination of 5-Aza-dC and MX Treatment Synergistically InducedApoptosis in A375 Melanoma Cells

To examine the consequence of MX targeting the AP sites produced by5-aza-dC, using flow cytometry of Annexin V-FITC, we analyzed andcompared the percentage of apoptotic cells induced by treatment with thecombination of 5-aza-dC and MX or drugs alone. When cells were treatedwith 5-aza-dC (5 M for 2 h) or MX alone (12.5 mM for 2 h and 3 mM for 24h), 97% of cells remained viable at 24 h after treatment. In contrast,when cells were incubated with the combination of 5-aza-dC and MX,5-fold more cells were killed by forcing target cells to go intoapoptosis (P<0.01). The MX-protentiated cytotoxicity of 5-aza-dC wasconsistent with the results obtained from the survival assays (FIGS.3-4). Similarly, enhanced induction of apoptosis was also observed incells treated with TMZ plus 5-aza-dC or in combination with MX (FIG. 5).Thus, the combined treatments as compared with single treatment resultin more effective apoptotic response in cells. FIG. 6 shows theexpression levels of protein markers of cell death in response to TMZ,MX, 5-aza-dC alone or in combination.

Caspase activation is the final common molecular event required forexecution of apoptosis in most biological systems. PARP is a cellularsubstrate that is cleaved by active caspase-3 during apoptosis. Thus,the levels of cleaved PARP act as a nuclear apoptotic landmark. Toexamine caspase activation, cell lysates obtained 24 hr after treatmentof A375 cells with either, 5-aza-dC, TMZ, or MX alone or thecombinations were analyzed for PARP cleavage. The increase in PARPcleavage activity was seen in cells treated with the combinations,indicating that the treatment-induced apoptosis was dependent oncaspase-3 protease activity. Western blot analysis also revealed anincrease in γH2AX in cells treated with TMZ and TMZ in combination witheither MX or 5-aza-dC or both. H2AX phosphorylation has beendemonstrated to be an early chromosome modification that is followed byapoptotic DNA fragmentation and constitutes an important step in thecourse of mammalian apoptosis. Our results showed that increased γH2AXwas concomitant with the induction of cleaved PARP. We consistentlypropose that increased apoptotic death observed in this study is relatedto the DNA DSBs induced by the blocking BER pathway. MGMT protein levelswere measured in cells to confirm that as an alkylating agent, TMZinhibits MGMT; 5-aza-dC as a demethylation agent does not affect theexpression of MGMT. Results indicate that the re-expression of MGMT inmelanoma cells by the combination of TMZ and 5-aza-dC is not theconcern.

Antitumor Activity of TMZ with 5-Aza-dC and MX In Vivo

Next, we tested the effect of TMZ with 5-aza-dC and MX on theprogression of established A375 melanoma xenograft tumors in nude mice(FIG. 9). We treated mice bearing s.c. tumors (˜100 mm³) with vehiclecontrol (PBS), TMZ (80 mg/kg), 5-aza-dC (0.75 mg/kg), and MX (2 mg/kg),and the combinations, ip injection, daily×3 days for 2 consecutivecycles. Treatment with TMZ alone had a minor effect on the overallgrowth of A375 tumors compared to the vehicle control. In contrast,further tumor growth in the mice treated with the combination of TMZwith MX or 5-aza-dC was prevented, and efficient inhibition of tumorgrowth was seen in mice treated with the combination of all three drugs(P<0.02); at day 15, tumor volume was only ⅙ of that in control mice.However, the inhibition of tumor growth using the MX, 5-azadCcombination was not optimal and needs to be pursued with additional doseand time course studies. As compared with control animals, no additivetoxicity (based on the assessment of body weight) was observed in micereceiving combined treatment.

General Methods Immunohistochemistry

Formalin-fixed and paraffin-embedded mice tissue sections are examinedfor BER proteins and active AKT, PTEN, and expression of Topo IIa usingthe 3,3′-diaminobenzidine kits (Ventana Medical Systems, Tucson, Ariz.).The slides are deparaffinized with xylin and graded alcohol and treatedwith citrate buffer (pH 6) for 20 min for antigen retrieval. The slidesare incubated with primary antibodies (1:100 dilution) at 4° C.overnight, followed by secondary antibody at room temperature for 1 hr.Sections are counterstained with hematoxylin and examined under themicroscope, with representative areas being photographed using a ×20objective.

Immunofluorescence Microscopy

Cells are grown on coverslips and treated with MX plus TMZ or with eachdrug separately for 24, 48, and 72 hrs. Both treated and untreated cellsare fixed in 2% paraformaldehyde and permeabilized with 0.2%Triton-100x. Cells are incubated with primary antibodies to proteinssuch as γH2AX (Upstate Biotechnology), topo II (Santa Cruz), or BERproteins and then followed by secondary antibodies conjugated to Alexa488 (green) or Alexa 633 (red), respectively (Molecular Probes). Imagesare digitally captured using an Olympus microscope equipped with adigital camera.

Western Blotting

Cell or tissue lysates (50 μg in buffer containing 1% NP40, 20 mM HEPES,4 mM EDTA, 1 mM phenylmethylsulfonyl fluoride, 50 μg/ml trypsininhibitor, 5 mM benzamidine, and 1 μg/ml each of aprotinin, leupeptin,and pepstatin) are separated by SDS-PAGE and electrotransferred ontonitrocellulose membranes. Blots are blocked with 5% nonfat dry milk in0.1% Tween 20 in PBS for 1 h at room temperature and incubated overnightat 4° C. with primary antibodies, according to the manufacturer'srecommended dilution, followed by incubation with secondary horseradishperoxidase-conjugated antibodies (Amersham Biosciences) for 1 h at 37°C. β-Actin is used as an internal standard for protein loading.Immunoreactive bands are visualized by enhanced chemiluminescence andsubsequent exposure to hyperfilm (X-ray film; Eastman Kodak).

Assessment of Apoptosis by Annexin V Staining

For annexin V-FITC staining, 1×10⁶ cells are washed twice with cold PBSand then resuspended in 1× binding buffer (10 mM HEPES[N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid]/NaOH, pH7.4, 140mM NaOH, 2.5 mM CaCl₂). The cells are incubated with annexin V-FITC (BDPharMingen, San Diego, Calif.) and 5 μg/mL propidium iodide (PI), andincubated for 15 minutes at room temperature in the dark per themanufacturer's instructions. The samples are analyzed by flow cytometrywithin 1 hour to determine the percentage of cells displaying annexin Vstaining (early apoptosis) or both annexin V and PI staining (lateapoptosis).

AP Site Assay

The AP sites are measured using ARP, which competitively reacts with MXto bind to an aldehyde group at AP sites. Thus, this reagent detectsonly MX-free AP sites. The assay is performed as previously describedwith minor modifications (24, 32-34). Briefly, cells (2×10⁶) are platedand exposed to TMZ or 5-aza-dC (with increasing concentrations) with orwithout MX. Cells are collected at 4 or 24 hr after treatment anddose-dependent AP sites are measured. Alternatively, for thetime-dependent assay, cells are exposed to drug at IC50 values with orwithout MX for a period of 72 hrs. Cells are harvested at 24, 48, and 72hr, respectively. After extracting by phenol (Fischer Scientific, FairLawn, N.J.) and chloroform (Sigma-Aldrich, St Louis, Mo.), DNA (10 μg)is incubated with 15 μl of 1 mM ARP (Dojindo Laboratories, Kumamoto,Japan) in 150 μl PBS solution at 37° C. for 15 min. DNA is thenprecipitated with 400 μl ice-cold ethanol (100%) at −20° C. for 20 minand washed with 70% ethanol. DNA is dried at room temperature for 30 minand then resuspended in TE buffer to achieve a final concentration of0.3 μg/100 μl. The ARP-labeled DNA is then heat-denatured at 100° C. for5 min, quickly chilled on ice and mixed with an equal amount of 2 Mammonium acetate. The DNA is then immobilized on BA-S 85 nitrocellulosemembrane (Schleicher and Schuell, Dassel, Germany) using a minifold IIvacuum filter device (Schleicher and Schuell, Dassel, Germany). Themembrane is baked at 80° C. for 1 hr and incubated with 0.25% BSA/PBScontaining streptavidin-conjugated horseradish peroxidase (BioGenex,SanRamon, Calif.) at room temperature for 40 min with gentle shaking.ARP-labeled AP sites are visualized by chemiluminescence (Amersham Corp,Piscataway, N.J.) followed by quantitative densitometry using NIH ImageJsoftware.

The Alkaline and Neutral Single Cell Gel Electrophoresis (Comet) Assay

The Comet assay is based on the ability of denatured, cleaved DNAfragments to migrate out of fixed cells under the influence of anelectric field. Undamaged DNA migrates slower and remains within theconfines of the nuclei when a current is applied. The single cell Cometelectrophoresis assay is performed using a Comet Assay kit (Trevigen,Gaithersburg, Md.). Approximately 5000 (in 50 al) cells after thetreatment are mixed with 250 al of 1% low melting point agarose in 1×PBSat 37° C. The mixture (75 al) is quickly pipetted onto a Comet slide(Trevigen, Gaithersburg, Md.) and allowed to solidify at 4° C. Slidesare immersed for 30 min in prechilled lysis buffer (2.5 mM sodiumchloride, 100 mM EDTA pH 10, 10 mM Tris Base, 1% sodium laurylsarcosinate, 0.01% Triton X-100) at 4° C. After lyses, slides areincubated for 20 min in alkali solution (0.3 M NaOH, 1 mM EDTA) at roomtemperature to allow unwinding of DNA and then subjected to both neutraland alkaline electrophoresis for the next 20 min. Comet in an individualcell is stained with Comet silver staining kit (Trevigen, Gaithersburg,Md.) and visualized using an on-line CCD camera. Fifty cells pertreatment are analyzed using NIH ImageJ software to generatequantitative and statistical data. Cellular DNA damage is expressed asthe “tail moment” that combines a measurement of the length of the DNAmigration and the relative DNA content therein.

Clonogenic Survival Assay

Cells (2000/dish) are plated and treated with TMZ or 5-aza-dC, with orwithout MX. After treatment, the drugs are removed, and fresh medium isadded to the cells for 7 days. Surviving colonies are stained withmethylene blue for 30 min at room temperature, and the coloniescontaining more than 50 cells are counted to generate survival curves.To assess drug-induced cytotoxicity, the ratio of the IC50 of theinitial drug alone to that obtained for the combination is calculated.This ratio is referred to as the DMF parameter and indicates the degreeof potentiation of cytotoxicity by the modulator.

Xenograft Studies

These studies will test the antitumor effect of TMZ alone and incombination with MX and decitabine on melanoma xenografts in athymicmice.

Tumor cells (5×10⁶) are injected into bilateral flanks of female athymicnude mice (6-8 weeks of age). When the volume of tumor nodules reached100-150 mm³, mice are randomly assigned to control or treatment groups(6-10 mice/group).

Tumor measurement: Tumors are measured with calipers using the formula:V=L (mm)×W² (mm)/2, where L is the largest diameter and W is thesmallest diameter of the tumor. Tumor measurements will be taken every 3days. The relative tumor volume (V/VO) is calculated by dividing themeasured tumor volume (V) by the initial tumor volume (VO) at day 0.

End point: Tumor responses are quantified by tumor regrowth delay, wheretumor growth delay=T2x−C2x; T2x and C2x represent the number of daysthat treated (T) and control (C) tumors take to double in size from theday of treatment, respectively.

Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, numerous equivalents to thecompounds and methods of use thereof described herein. Such equivalentsare considered to be within the scope of this invention and are coveredby the following claims. All patents, publications, and references citedin the present application are herein incorporated by reference in theirentirety.

Having described the invention, the following is claimed:
 1. A method oftreating cancer in a subject comprising: administering to the subject atherapeutically effective amount of an antimetabolite agent that inducesformation of AP sites in cancer cells of the subjects and an amount APendonuclease inhibitor effective to potentiate the cytotoxicity of theantimetabolite agent to the cancer cells.
 2. The method of claim 1, theAP endonuclease inhibitor is selected from group consisting ofmethoxyamine, O-benzylohydroxylamine; ethyl aminooxyacetate;aminooxyacetic acid; ethyl aminooxyacetate; H₂NOCHMeCO₂H;carboxymethoxyamine; aminooxyacetic acid; HN═C(NH₂)SCH₂CH₂ONH₂;H₂NO(CH₂)₃SC(NH₂)═NH; MeOC(O)CH(NH₂)CH₂ONH₂; H₂NOCH₂CH(NH₂)CO₂H;canaline; H₂NO(CH₂)₄ONH₂; O-(p-nitrobenzyl)hydroxylamine;2-amino-4-(aminooxymethyl)thiazole; 4-(aminooxymethyl)thiazole;O,O′-(o-phenylenedimethylene)dihydroxylamine; 2,4-dinitrophenoxyamine;O,O′-(m-phenylenedimethylene)dihydroxylamine;O,O′-(p-phenylenedimethylene)dihydroxylamine; H₂C═CHCH₂ONH₂;H₂NO(CH₂)₄ONH₂; H₃C—(CH₂)₁₅—O—NH₂,2,2′-(1,2-ethanediyl)bis(3-aminooxy)butenedioic acid dimethyl diethylester;

a compound having a structure of Formula I:

wherein X is O or NH, Y is O, S, or NH, Z is absent or represents O, S,or NH, and R represents a hydrogen or a hydrocarbon moiety, andpharmaceutically acceptable salts thereof.
 3. The method of claim 1, theAP endonuclease inhibitor comprising methoxyamine.
 4. The method ofclaim 1, the antimetabolite agent comprising a nucleoside analog.
 5. Themethod of claim 4, the nucleoside analog comprising5-aza-2′-deoxycytidine.
 6. The method of claim 1, further comprisingadministering an anticancer agent to the subject.
 7. The method of claim6, the anticancer agent comprising an alkylating agent.
 8. The method ofclaim 1, wherein the amount of antimetabolite agent is subtherapeuticwhen administered in the absence of the AP endonuclease inhibitor. 9.The method of claim 1, wherein the amount of the AP endonucleaseinhibitor is an amount sufficient to sensitize the cancer cells withoutcausing undue sensitization of normal cells.
 10. The method of claim 1,wherein the subject is selected as having a cancer at least partiallyresistant to treatment with antimetabolite agent alone, and wherein theAP endonuclease inhibitor is administered in an amount effective topotentiate the activity of the antimetabolite agent and overcome theresistance.
 11. The method of claim 1, wherein said cancer is selectedfrom the group consisting of carcinomas, melanomas, sarcomas, lymphomas,leukemias, astrocytomas, gliomas, malignant melanomas, chroniclymphocytic leukemia, lung cancers, colorectal cancers, ovarian cancers,pancreatic cancers, renal cancers, endometrial cancers, gastric cancers,liver cancers, head and neck cancers, and breast cancers.
 12. A methodof treating cancer in a subject comprising: administering to the subjecta therapeutically effective amount of an antimetabolite agent thatinduces formation of AP sites in cancer cells of the subjects and anamount of methoxyamine effective to potentiate the cytotoxicity of theantimetabolite agent to the cancer cells.
 13. The method of claim 12,the antimetabolite agent comprising a nucleoside analog.
 14. The methodof claim 13, the nucleoside analog comprising 5-aza-2′-deoxycytidine.15. The method of claim 12, further comprising administering analkylating agent to the subject.
 16. The method of claim 12, wherein theamount of antimetabolite agent is subtherapeutic when administered inthe absence of the methoxyamine.
 17. The method of claim 12, wherein theamount of the methoxyamine is an amount sufficient to sensitize thecancer cells without causing undue sensitization of normal cells. 18.The method of claim 12, wherein the subject is selected as having acancer at least partially resistant to treatment with antimetaboliteagent alone, and wherein the methoxyamine is administered in an amounteffective to potentiate the activity of the antimetabolite agent andovercome the resistance.
 19. The method of claim 12, wherein said canceris selected from the group consisting of carcinomas, melanomas,sarcomas, lymphomas, leukemias, astrocytomas, gliomas, malignantmelanomas, chronic lymphocytic leukemia, lung cancers, colorectalcancers, ovarian cancers, pancreatic cancers, renal cancers, endometrialcancers, gastric cancers, liver cancers, head and neck cancers, andbreast cancers.
 20. A method of treating cancer in a subject comprising:administering to the subject a therapeutically effective amount of anantimetabolite agent and methoxyamine, the antimetabolite agentcomprising a nucleoside analog that induces formation of AP sites incancer cells of the subject and the methoxyamine being administered atan amount effective to potentiate the cytotoxicity of the nucleosideanalog to the cancer cells.
 21. The method of claim 20, the nucleosideanalog comprising 5-aza-2′-deoxycytidine.
 22. The method of claim 20,further comprising administering an alkylating agent to the subject. 23.The method of claim 20, wherein the amount of the methoxyamine is anamount sufficient to sensitize the cancer cells without causing unduesensitization of normal cells.
 24. The method of claim 20, wherein thesubject is selected as having a cancer at least partially resistant totreatment with antimetabolite agent alone, and wherein the methoxyamineis administered in an amount effective to potentiate the activity of theantimetabolite agent and overcome the resistance.
 25. The method ofclaim 20, wherein said cancer is selected from the group consisting ofcarcinomas, melanomas, sarcomas, lymphomas, leukemias, astrocytomas,gliomas, malignant melanomas, chronic lymphocytic leukemia, lungcancers, colorectal cancers, ovarian cancers, pancreatic cancers, renalcancers, endometrial cancers, gastric cancers, liver cancers, head andneck cancers, and breast cancers.